Method for calibrating and verifying the attitude of a compass

ABSTRACT

A method for calibrating the attitude of a compass in relation to the platform on which the compass is installed. The compass includes an attitude determining device and an optical sighting device and the compass is integrally mounted on a platform. The method includes the steps of determining the angle between the optical sighting device and the attitude determining device, determining the attitude between the optical sighting device and the platform, and determining the attitude between the attitude determining device and the platform.

FIELD OF THE INVENTION

This present invention relates generally to systems for calibrating andverifying the attitude and azimuth of a compass in relation to theplatform on which the compass is installed which is particularlyapplicable to an Armored Fighting Vehicle (AFM).

BACKGROUND OF THE INVENTION

Compass systems including electronic magnetic compass systems are wellknown and are an essential component of Armored Fighting Vehicles (AFV)and the like. The purpose of the compass is to determine the, attitudeand azimuth of the vehicle to which the compass is attached. An exampleof such an electronic magnetic compass system is described in U.S. Pat.No. 4,687,772 to Sobel.

Prior art systems utilize various devices including magnetometers andgeomagnetic sensors to measure the travelling direction of a vehicle.Sobel, for example, describes an electronic magnetic compass systemwhich includes a non-pendulous triaxial magnetometer, sensors fordetermining the pitch and roll of the vehicle body and an anglemeasuring device to determine the angle rotation between the hull andthe turret of the tank.

A disadvantage of such systems is that they tend to be expensive toinstall, sensitive and are restricted to determining the attitude of thecompass with respect to the vehicle. The compass readings do notaccurately reflect an elevating object, such as the tank cannon.

Commonly today, antennas are used to collect data from GPS satellitesencircling the globe to determine the azimuth and elevation of avehicle. However, the problem of phase differences may lead to anincorrect calculation of the azimuth and elevation.

SUMMARY OF THE INVENTION

The present invention provides a method for calibrating the attitude ofa compass in relation to the platform on which the compass is installed.

The present invention also provides a method for verifying the attitudeand azimuth of a compass in relation to the platform on which thecompass is installed.

In addition, a method is also provided for determining the azimuth of atarget from a platform remotely located from said target.

There is thus provided, in accordance with a preferred embodiment of thepresent invention, a method for calibrating the attitude of a compass inrelation to the platform on which the compass is installed. The compassincludes an attitude determining device and an optical sighting deviceand the compass is integrally mounted on a platform. The method includesthe steps of:

determining the angle between the optical sighting device and theattitude determining device;

determining the attitude between the optical sighting device, and theplatform; and

determining the attitude between the attitude determining device and theplatform.

Furthermore, in accordance with a preferred embodiment of the presentinvention, the compass further includes a tilt sensor and the methodfurther includes the step of determining the elevation of the compassutilizing the tilt sensor.

In addition, in accordance with a preferred embodiment of the presentinvention, the platform includes a supporting body, a rotating componentcoupled to the supporting body, the rotating component having a directview optical device attached thereto, and a measuring device fordetermining the relative angle between the supporting body and therotating component.

Furthermore, in accordance with a preferred embodiment of the presentinvention, the supporting body is independently movable in relation tothe rotating component. The compass is attached to the rotatingcomponent.

Furthermore, in accordance with a preferred embodiment of the presentinvention, the step of determining the attitude between the attitudedetermining device and the platform includes the steps of:

a) sighting a first remote object using the optical sighting device;

b) recording a first angle (α₁) between the rotating component and thesupporting body and recording a first pitch (p₁) and a first roll (r₁)of the compass;

c) rotating the rotating component to sight the remote object via thedirect view optical device;

d) recording a second angle (α₂) between the rotating component and thesupporting body and recording a second pitch (p₂) and a second roll (r₂)of the compass;

e) rotating the rotating component by an angle (β);

f) recording the angle α_(k) between the rotating component and thesupporting body and the pitch (p_(k)) and the roll (r_(k) of thecompass;

g) repeating steps e) and f) a plurality of N times,

h) calculating the pitch and roll of the compass with respect to therotating component;

i) calculating the yaw of the compass with respect to the rotatingcomponent.

Furthermore, in accordance with a preferred embodiment of the presentinvention, N≧5. The angle (β) is approximately equal to 360°/N

In addition, there is provided, in accordance with a preferredembodiment of the present invention a method for verifying the attitudeof a compass. The compass includes an attitude determining device, atilt sensor and an inertial sensor. The method includes the steps of:

determining the attitude of the compass with reference to the earth'saxis from the attitude determining device; and

determining the tilt of the compass from the tilt sensor;

determining the angular velocity of the compass from the inertialsensor;

determining a predicted azimuth value from the angular velocity and thecompass attitude; and

comparing the azimuth of the compass, obtained from the step ofdetermining the attitude of the compass with reference to the earth'saxis, with the predicted azimuth value, and comparing the elevation ofthe compass, obtained from the step of determining the attitude of thecompass with reference to the earth's axis with the elevation obtainedfrom the step of determining the tilt, thereby verifying the attitude ofthe compass.

In addition, there is provided, in accordance with a preferredembodiment of the present invention, a method for verifying the azimuthof a compass. The compass includes an attitude determining device and aninertial sensor. The method includes the steps of:

determining the attitude of the compass with reference to the earth'saxis from the attitude determining device; and

determining the angular velocity of the compass from the inertialsensor;

determining a predicted azimuth value from the angular velocity and thecompass attitude; and

comparing the azimuth of the compass, obtained from the step ofdetermining the attitude of the compass with reference to the earth'saxis, with the predicted azimuth value.

Furthermore, in accordance with a preferred embodiment of the presentinvention, the compass further includes a tilt sensor and the methodfurther includes the step of determining the elevation of the compassutilizing the tilt sensor.

Additionally, there is provided, in accordance with a preferredembodiment of the present invention, a method for verifying the azimuthof a compass. The compass includes an attitude determining device and antilt sensor. The method includes the steps of:

determining the attitude of the compass with reference to the earth'saxis from the attitude determining device; and

determining the elevation of the compass from the inertial sensor;

determining a predicted azimuth value from the elevation and the compassattitude; and

comparing the azimuth of the compass, obtained from the step ofdetermining the attitude of the compass with reference to the earth'saxis, with the predicted azimuth value.

In addition, there is provided, in accordance with a preferredembodiment of the present invention, a method for determining theazimuth of a target from a platform remotely located from the target.The platform includes a base, a rotating component connected to thebase, an elevating component connected to the rotating component, anattitude determining device attached to the rotating component and arangefinder connected to the elevating component.

The method includes the steps of:

a) determining the attitude of the platform from the attitudedetermining device;

b) determining the distance from the platform to the target using therangefinder;

c) assuming a first iteration value of elevation α1 of the elevatingcomponent;

d) determining an assumed position N_(a), E_(a)) and height h_(a) of thetarget from the attitude of the platform and the distance;

e) obtaining the height (h_(dtm)) for the target from Digital TerrainMap (DTM) data

f) comparing the calculated height h_(a) wit the height (h_(dtm));

g) if height h_(a) is not approximately equal (within predeterminedparameters) to h_(dtm);

i) select a second iteration value of elevation α2; and

ii) repeat steps d)-f).

In addition, there is also provided, in accordance with a preferredembodiment of the present invention, a method for determining theazimuth of an elevating component connected to a rotation component, therotating component connected to a platform. The method includes thesteps of:

determining the azimuth of the rotating component;

calculate the elevation of the rotating component utilizing the tiltsensor; and

calculating the elevation of the elevating component according to themethod described hereinabove thereby to determine the azimuth.

Additionally, in accordance with a preferred embodiment of the presentinvention, the attitude determining device includes a plurality ofantennas having a common longitudinal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with theappended drawings in which:

FIG. 1 is a schematic block diagram illustration of the main componentsof the compass unit and processing unit associated therewith,constructed and operative in accordance with a preferred embodiment ofthe present invention;

FIG. 2 is a schematic illustration of the compass of the system of FIG.1;

FIGS. 3A and 3B are schematic top elevational views of an AFV (tank) towhich a sensing unit of FIG. 2 has been fixed;

FIG. 4 is a flow chart illustration of the method of calibration of theazimuth and the AFV pitch and roll;

FIG. 5 is a schematic illustration of an AFV (tank) within a contouredterrain;

FIG. 6 is a flow chart diagram to illustrate the method of calculationusing a rangefinder together with DTM data;

FIG. 7 is a schematic illustration of the relationship between thephases of the signals from the satellites received by two antennas; and

FIG. 8 is a flow chart diagram to illustrate the method of verifying theattitude of the compass of the system of FIG. 1.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Reference is made to FIG. 1, which is a schematic block diagramillustration of the main components of the calibration and verificationsystem, generally designated 10, constructed and operative in accordancewith a preferred embodiment of the present invention. Calibration andverification system 10 comprises a compass unit 12 coupled to a controland processing unit 14. The compass unit 12 is installable on aplatform, such as a vehicle, for example, an Armored Fighting Vehicle(AFV) or Armored Combat Vehicle (ACV).

In a preferred embodiment, the compass unit 12 comprises a plurality ofantennas 16 which are coupled to a GPS receiver 18 for receiving datafrom the array of satellites 20 circling the globe.

Compass unit 12 further comprises a processor 22, a communications unit24 and a tilt sensor 26. As seen in FIG. 2, compass unit 12 furthercomprises an optical eyepiece 28 attached to one side of the compassunit 12. Alternatively, the compass unit 12 further comprises aninertial sensor 27.

The angle γ between the axis of the eyepiece 28 and the antennas 16 canbe accurately determined during the manufacture of the compass unit 12.The value of angle γ is used to determine the attitude of the compassunit 12 in relation to the platform on which the compass is installed.

Before installation on its platform, each compass unit 12 is accuratelycalibrated. An exemplary method of calibrating the compass unit 12includes collecting of GPS data over a period of several hours(preferably at least 6 hours) on a fixed base in laboratory conditions.The GPS data is processed in order to obtain a reading for the azimuthof the particular compass unit 12 being calibrated. The calculatedazimuth reading for the compass unit 12 is then compared with the exactknown azimuth of the fixed base in the laboratory in order to accuratelydetermine the compensation adjustment required for each compass unit 12.A method for verifying the attitude and azimuth of the compass whichovercomes the problem of phase differences (see FIG. 7) is describedhereinbelow.

Control and processing unit 14 is any suitable processing unit known inthe art and, for example, may comprise communication ports 30, such asRS 232 and RS 242 connected to a computer unit 32 having a keyboard 34and display screen 36.

Reference is now made to FIGS. 3A and 3B, which are schematic topelevational views of an AFV, generally referenced 40, to which a compassunit 12 has been fixed. Reference is also made to FIG. 4, which is aflow chart illustration of the method of calibration of the attitude ofthe compass 12 in relation to the AFV platform 40. The method includestaking a set of N readings at different compass points. Preferably, N≧25and the angle β between each reading (βis approximately equal to360°/N). Thus, for example if N=6, readings are taken approximatelyevery 60° (360/6).

For the purposes of example only and without limiting the presentapplication, the following description refers to an AFV 40, as anexemplary platform.

Prior to installation on the platform, the compass unit 12 is accuratelycalibrated on a fixed base within the laboratory (step 202), asdescribed above.

The angle γ between the axis of the eyepiece 28 and the antennas 16 isalso determined at time of manufacture (step 204).

The compass unit 12 is fixed (step 206) preferably on the rotatableturret 42 of the AFV 40. AFV 40 also includes a hull 44 and a cannon 46.The compass unit 12 may be fixed at any suitable location on the turret42 and is shown as being generally perpendicular to the longitudinalaxis 48 of the turret 42 for clarity. The longitudinal axis of the AFVhull 44 is referenced 50.

A suitable remote object 52, such as tree, for example, is sighted usingthe optical eyepiece 28 (step 208). The distance to remote object 52should be as large as possible. The angle α₁ between the turret 42 andthe hull 44, (angle between axis lines 48 and 50) and the pitch (p₁) androll (r₁) of the compass 12 are recorded (step 210) (N=1).

The turret 42 is then rotated (step 212) until the object (tree 52) isin the sights of the direct view optical device which is generallyaffixed to the cannon (FIG. 3B). The turret/hull angle α₂ between axislines 48 and 50 and the pitch (p₂) and roll (r₂) of the compass 12 arerecorded (step 214) (N=2).

A further N−2 readings of the turret/hull angle α_(N) and pitch (p_(N))and roll (r_(N)) are taken, each time rotating the turret by an angle β,where β≈360°/N (step 216).

After N steps (say N=6) the following data is available:

h) a) a vector B of N turret/hull angles:

B=(α₁, α₂, α₃, . . . , α_(N))^(T),

i) b) a vector P of N sensor pitch angles:

P=(p₁, p₂, p₃, . . . , p_(N))^(T),

c) a vector R of N sensor roll angles:

R=(r₁, r₂, r₃, . . . , r_(N))^(T).

The vectors B, P and R are then used to the calculate the pitch{circumflex over (p)}_(S) and roll {circumflex over (r)}_(s) of thecompass With respect to the turret (step 218), and the yaw ŷ_(S) of thecompass with respect to the turret (step 220).

The angles P and R are measured using the East/North/Up coordinatesystem. The unknown values are the tank attitude angles p_(T), r_(T) andy_(T). Calculation of the Compass Pitch and Roll

The compass pitch may be estimated as the average value of the measuredpitch on the full turret rotation (0-360 degrees). This is based on thefact that the average value will be zero if there is no compass pitch.Accordingly, the least square estimation is used for calculation ofdependency of the measured pitch on the hull—turret angle:

p(β)={overscore (Q)}[1 cos(β)sin(β)]^(T)  (1)

The vector {right arrow over (Q)}=(Q_(p0) Q_(p1) Q_(p2))^(R) iscalculated according to the formula:

{right arrow over (Q)}=(Φ^(T)Φ)Φ^(T) P.  (2)

The matrix Φ consists of N following rows: [1 cos(β₁)sin(β_(i))].

The compass pitch {circumflex over (p)}_(S) is defined from (1) as{circumflex over (p)}_(s)=Q₀.

The compass roll may be defined similar to the pitch (which isapplicable in the case of attitudes where p_(T), r_(T) is less than10°):

r(β)={right arrow over (U)}[1 cos(β)sin(β)]^(T),   (3)

{overscore (U)}=(Φ^(T)Φ) Φ^(T) R, {circumflex over (r)} _(S) =U ₀.  (4)

Calculation of the Compass Yaw

The first two steps of the calibration procedure are used forcalculation of the compass yaw in relation to the turret. For thispurpose, two matrix equations are constructed in order to get thedirection to the remote point

The first step gives:

C(A_(rg))=C(A_(T))C _(r)(β₁)C(A_(S))C(α).  (5)

The second step gives:

C(A_(rg))=C(A_(T))C _(r)(β₂).  (6)

The formulas (5) and (6) use the following notation:

A_(T)=(0 p_(T)r_(T))^(T) —attitude of the tank (the yaw is ignored);

A_(s)=(y_(S) p_(S) r_(S))^(T) —attitude of the compass in the turretcoordinates;

C({overscore (a)}) is rotation matrix, corresponding to any attitudevector (for example. A_(T) or A_(S)): ${{Cy}(\alpha)}:=\begin{pmatrix}{\cos (\alpha)} & {- {\sin (\alpha)}} & 0 \\{\sin (\alpha)} & {\cos (\alpha)} & 0 \\0 & 0 & 1\end{pmatrix}$ ${{Cp}(\alpha)}:=\begin{pmatrix}1 & 0 & 0 \\0 & {\cos (\alpha)} & {- {\sin (\alpha)}} \\0 & {\sin (\alpha)} & {\cos (\alpha)}\end{pmatrix}$ ${{Cr}(\alpha)}:=\begin{pmatrix}{\cos (\alpha)} & 0 & {\sin (\alpha)} \\0 & 1 & 0 \\{- {\sin (\alpha)}} & 0 & {\cos (\alpha)}\end{pmatrix}$

C(a)=Cy(a₀)−Cp(a₁)−Cr(a₂)

The left hand side of equations (5), (6) correspond to the same remotepoint. Its yaw may be found from matrix C(A_(rg)) as:$Y_{rg} = {{arc}\quad {{{tg}\left( {- \frac{C_{0,1}}{C_{1,1}}} \right)}.}}$

Thus, yaw y_(S) may be found as the angle that provides the followingequivalence:

C(A _(T))C _(r)(β₁)C(A _(S))C(α)=C(A_(T))C _(r)(β₂).  (7)

(y_(s) is included in A_(s))

The above calculations generate the azimuth (yaw), pitch and roll of thecompass with respect to the turret. These values for the compass withrespect to the turret do not necessarily relate to the cannon. This isespecially so if the AFV is not “on the level” and subject to roll. Thatis, the azimuth of the cannon only equals the azimuth of the turret ifthe AFV is horizontal.

To accurately fix the target, it is essential that the pitch, roll andyaw (p_(c), r_(c), y_(c)) of the cannon are accurately known.

The correct pitch, roll and yaw of the cannon can be calculated by oneof several methods known in the art. For example, by adding a transducerto the cannon, the angle of the cannon itself can be measured.Alternatively, by integrating the cannon and the turret with the firecontrol system of the AFV, the value of the pitch, roll and yaw of thecannon can be obtained. It is difficult and expensive to integrate thecompass with the platform sensors. Furthermore, the transducer needs tobe able to withstand the rugged conditions of the AFV and requiresadditional connections which further complicates the control system.

Applicant has realized that by using a rangefinder together with mapdata available from Digital Terrain Model (DTM) maps, it is possible toaccurately determine the correct pitch, roll and yaw of the compass withrespect to the cannon itself for any AFV without the necessity offitting expensive and complicated transducers and or special integrationof the fire control system.

Reference is now made to FIGS. 5 and FIG. 6. FIG. 5 is a schematicillustration of an AFV (tank) within a contoured terrain, generallydesignated 62, and FIG. 6 is a flow chart diagram to illustrate themethod of determining the azimuth of a target (using a rangefindertogether with DTM data) from the AFV platform, the target being remotelylocated from the AFV platform. FIG. 5 schematically illustrates (boxABCD) the area over which the turret of AFV rotates. Box PQRSillustrates a sectional slice taken along line P-S. T is a target havinga height h above the level of the turret (line P-S). Angle α is theangle of elevation of the cannon above line P-S. R is the arc distancefrom the cannon to the target T.

As the AFV 60 traverses the terrain 62, the roll and pitch of the AFVchanges and consequently, the roll and pitch of the turret and cannonchange.

At any position P, the attitude of the AFV can be calculated (asdescribed hereinabove with respect to FIG. 4)—step 302. Using arangefinder, the distance R to the target T is determined (step 304).

An assumed value of the position and height of the target T can bedetermined knowing the attitude of the AFV 60, the distance R to thetarget T and the angle of elevation α. The angle α is determined byiteration.

Thus, to determine the Northing and Easting positions and the height oftarget T, a first iteration is made (step 306), assuming an angle α′,say 5 °.

Knowing the distance R, the attitude of AFV 60 and the angular directionof the cannon, a first estimation (assumed) value of thenorthing/easting (N_(a), E_(a)) (step 308) and an assumed height h_(a)of target T can be calculated (step 310).

Using the DTM map, the height (h_(map)) for the assumed northing/easting(N_(a), E_(a)) of T (from step 308) can be found (step 312). The valuesof h_(map) and h′ are compared (step 314) and if h_(map) is notapproximately equal (within predetermined parameters) to h′ (query box316), then a further iteration for the elevation angle α′ (step 318) ismade and steps 308-316 are repeated (step 320) until h_(map) isapproximately equal to h′ (within predetermined parameters) (step 322).Thus, the angle of elevation of the cannon can be determined.

Reference is now made to FIG. 7 which is a schematic illustration of therelationship between the phases of the signals from the satellitesreceived by two antennas, referenced 16 a and 16 b, at either end of thecalibration compass unit 12, a distance B apart. W1 and W2 illustratethe incoming wavelengths from one of the GPS satellites encircling theglobe. In practice each of the antennas receives input from 8-10satellites at a time. The quality of the signals from these satellitesvary. The signal received by satellite 16 a arrives a short time afterthe signal received by satellite 16 b. The phase difference φ can becalculated from: $\phi = \frac{b\quad \cos \quad \alpha}{\lambda}$

Where λ is the wavelength of the signal.

For an exemplary calibration compass unit 12 m, where B=60 cm and λ=19cm and α=0, the phase difference φ=3.1. However phase differences φ areonly referred to by the figure to the right of the decimal point (theinteger being dropped) That is, in the example, the phase difference φis recorded as 0.1. Since it is not known whether the phase difference φis 3.1 or 2.1 or 1.1, for example, there are several possible answersfor the angle α. Thus, phase difference φ=N+φ′, where N is an integerhaving value: 3≦N≧−3, that is N has 7 possible values. Since there arethree dimensions and assuming that 4 satellite signals are received, thenumber of possible solutions is approximately 1200 (7³*4).

Using common sense and observation, it is possible by eliminatingobviously impossible answers, to reduce the number of possible solutionsto a more reasonable number of say about 10 ‘likely’ solutions. Thenusing the known attitude, b can be calculated. However, attitudedetermination does not provide 100% accuracy since it is still possibleto obtain several probable results.

The following table is an illustrative example of possible resultsobtained.

TABLE 1 Azimuth Elevation Calc, b a) 90°  1° 61.0 b) 95° 10° 60.5

In this case, either a) or b) may be correct, and the most likelysolution is b) since the calculated value of b (60.5) is closer to theknown value of 60 cm.

A method for verifying the attitude and azimuth of the compass whichreduces the degree of ambiguity and allows for a higher degree ofaccuracy to be obtained in overcoming the problem of phase differencesis now described.

Referring again to FIG. 1, the compass unit 12 comprises a plurality ofantennas 16 which receive GPS data from the array of satellites 20circling the globe a tilt sensor 26 and alternatively an additionalsensor such as an inertial sensor 27.

By utilizing the tilt sensor 26 and the inertial sensor 27, the attitudeand azimuth of the compass unit 12 can be independently verified.

The data received by the plurality of antennas 16 (from the GPS) allowsthe attitude (azimuth and elevation) to be determined. The tilt sensor26, using gravity, measures the elevation of the compass. The inertialsensor 27 allows the angular velocity a of the compass to be determined.

Thus, to verify the azimuth of the compass, a comparison is made betweenthe predicted azimuth value obtained from the inertial sensor with theazimuth value obtained from the GPS satellites. In addition, to verifythe attitude of the compass, a comparison is also made between theelevation of said compass, obtained from the GPS satellites with theelevation obtained from the tilt sensor 26. The method is described withrespect to FIG. 8.

The attitude (Ya, Pa, Ra) of the compass with reference to the earth'saxis is determined from the data received from the antennas (step 352).The tilt of the compass is determined from the tilt sensor (step 354).

The predicted elevation angle (αp) is then calculated from the compassattitude (step 356)

The velocity of the compass is determined from the inertial sensor (step358). The predicted azimuth value is then calculated from the velocity(Vs) and the compass attitude (step 360).

The angle value α₀, say, determined from the GPS is adjusted by ω., asfollows (t=time), to give a predicted value α_(p), as follows:

α_(p=α) ₀+ωt

The values of α₀+ω are then filtered through a Kalman filter to give afurther estimate (α_(p)′). The values of α_(p)′ and Δ_(p) should beapproximately the same. Thus, in the example of the above Table, ifα₀=90°, for a value of ω=0, α_(p)=90°. Thus, from the two possiblevalues (a or b) shown in Table 1 (above), a is the more probable correctanswer.

Finally, to verify the azimuth of the compass, the values obtained fromthe step of determining the attitude of the compass with reference tothe earth's axis (step 352) is compared (step 362) with the predictedazimuth value (step 360). To verify the attitude, the elevation of thecompass obtained from the step of determining the attitude of saidcompass (step 356) is compared (step 364) with the elevation obtainedfrom the tilt sensor (step 354).

Thus, the degree of ambiguity reduced and a higher degree of accuracy isobtained.

It will be appreciated that the present invention is not limited by whathas been described hereinabove and that numerous modifications, all ofwhich fall within the scope of the present invention, exist. Rather thescope of the invention is defined by the claims, which follow:

What is claimed is:
 1. A method for verifying the attitude of a compass,the compass comprising an attitude determining device, a tilt sensor andan inertial sensor, the method comprising the steps of: determining theattitude of said compass with reference to the earth's axis from saidattitude determining device; and determining the tilt of said compassfrom said tilt sensor; determining the angular velocity of said compassfrom said inertial sensor; determining a predicted azimuth value fromsaid angular velocity and said compass attitude; and comparing theazimuth of said compass, obtained from said step of determining theattitude of said compass with reference to the earth's axis, with thepredicted azimuth value, and comparing the elevation of said compass,obtained from said step of determining the attitude of said compass withreference to the earth's axis with the elevation obtained from said stepof determining the tilt, thereby verifying the attitude of said compass.2. The method according to claim 1, wherein said attitude determiningdevice comprises a plurality of antennas having a common longitudinalaxis.
 3. A method for verifying the azimuth of a compass, the compasscomprising an attitude determining device and an inertial sensor, themethod comprising the steps of: determining the attitude of said compasswith reference to the earth's axis from said attitude determiningdevice; and determining the angular velocity of said compass from saidinertial sensor; determining a predicted azimuth value from said angularvelocity and said compass attitude; and comparing the azimuth of saidcompass obtained from said step of determining the attitude of saidcompass with reference to the earth's axis, with the predicted azimuthvalue.
 4. A method according to claim 3, wherein said compass furthercomprises a tilt sensor and wherein the method further comprises thestep of: determining the elevation of said compass utilizing said tiltsensor.
 5. The method according to claim 3, wherein said attitudedetermining device comprises a plurality of antennas having a commonlongitudinal axis.
 6. A method for determining the azimuth of a targetfrom a platform remotely located from said target, said platformcomprising a base, a rotating component connected to the base, anelevating component connected to the rotating component, an attitudedetermining device attached to the rotating component and a rangefinderconnected to the elevating component, the method comprising the stepsof: a) determining the attitude of said platform from the attitudedetermining device; b) determining the distance from the distance fromthe platform to the target using said rangefinder; c) assuming a firstiteration value of elevation α1 of the elevating component; d)determining an assumed position (N_(a), E_(a)) and height h_(a) of thetarget from the attitude of said platform and said distance; e)obtaining the height (h_(dtm)) for said target from Digital Terrain Map(DTM) data; f) comparing the calculated height h_(a) with the height(h_(dtm)); g) if height h_(a) is not approximately equal (withinpredetermined parameters) to h_(dtm); i) select a second iteration valueof elevation α2; and ii) repeat steps d)-f).
 7. The method according toclaim 6, wherein said attitude determining device comprises a pluralityof antennas having a common longitudinal axis.
 8. A method fordetermining the azimuth of an elevating component connected to arotating component, said rotating component connected to a platform, themethod comprising the steps of: determining the azimuth of the rotatingcomponent; calculate the elevation of said rotating component utilizingthe tilt sensor; and calculating the elevation of the elevatingcomponent according to the method of claim 6; thereby to determine theazimuth.